1. Field of the Invention
The present invention relates to a battery voltage measurement device for measuring a voltage of stacked rechargeable batteries (a battery pack) which is mounted in an apparatus driven by the rechargeable batteries, such as an electric vehicle or the like.
2. Description of the Related Art
As a low-pollution vehicle designed for the purpose of solving environmental problems and energy problems, an electric vehicle such as an HEV (hybrid electric vehicle) and a PEV (pure electric vehicle) has received a great deal of attention up to the present. The electric vehicle has rechargeable batteries mounted therein, and the electric power of the rechargeable batteries drives an electric motor so as to run the electric vehicle. The electric vehicle has a high-voltage circuit for driving the electric motor and a low-voltage circuit for driving various electronic devices such as acoustic equipment, lighting devices, and an electronic controller (e.g., ECU; electronic control unit). The high-voltage circuit includes an inverter for driving an electric motor, and the inverter controls and drives the electric motor.
In a battery control section of such an electric vehicle, in order to obtain an output state of the rechargeable batteries which stably supplies electric power to the electric motor, it is necessary to use a battery voltage measurement device to accurately measure a battery voltage of each battery block of the battery pack.
FIG. 4 is a circuit diagram illustrating an exemplary structure of a conventional battery voltage measurement device 100. In FIG. 4, the battery voltage measurement device 100 includes: a plurality of switches 120 in which each pair of adjacent switches 120 sequentially selects two corresponding output terminals 111a of a battery block 111 included in a battery pack 110; a capacitor 130 for storing (copying) a designated battery voltage; switches 140 for selectively applying the battery voltage stored in the capacitor 130 to a differential amplifier 150; the differential amplifier 150 for differentially amplifying the stored battery voltage which is input thereto via the switches 140; and an A/D converter 160 for performing an A/D conversion of the voltage output from the differential amplifier 150.
The battery pack 110 includes a plurality of serially-connected battery blocks 111. A value of a voltage output from one battery block 111 (battery module) is, for example, about DC 20 V. The maximum value of a voltage output from all of the serially-stacked battery blocks 111 is about DC 400 V.
Each pair of adjacent switches 120 is connected to the two corresponding output terminals 111a of each of the plurality of battery blocks 111.
The capacitor 130 has electrodes connected to a pair of conductor lines 141a and 141b laid between the switches 120 and the switches 140. The capacitor 130 temporarily stores a battery voltage of each of the battery blocks 111, which is transferred via two designated switches 120 to the capacitor 130.
Each of the switches 140 is connected to one of the two input terminals of the differential amplifier 150 and serves to connect the differential amplifier 150 to the capacitor 130 or disconnect the differential amplifier 150 from the capacitor 130. On/Off control of the plurality of switches 120 and the switches 140 is performed by a switching controller (not shown), e.g., a microcomputer.
With the above-described structure, at first, in order to store (copy) a battery voltage of a first battery block 111 in (into) the capacitor 130, each of the switches 120 connected to one of the two output terminals 111a of the first battery block 111 is turned on. At this time, the switches 140 are turned off to disconnect the capacitor 130 from both of the two input terminals of the differential amplifier 150.
Next, all the switches 120 are turned off to disconnect the capacitor 130 from all of the battery blocks 111, and then the switches 140 are turned on so as to input the battery voltage of the first battery block 111, which is stored in the capacitor 130, to the differential amplifier 150. Data corresponding to the battery voltage differentially-amplified, for example, from DC 20 V to DC 5 V in an input voltage range of the A/D converter 160, by the differential amplifier 150 is A/D-converted by the A/D converter 160. The A/D-converted battery voltage data is read by, for example, a microcomputer (not shown) in a subsequent stage.
However, in the conventional battery voltage measurement device 100, in the case where the battery voltage of the designated battery block 111 is stored in the capacitor 130 and all of the switches 120 are turned off at the time of measuring the battery voltage, when the switches 140 are turned on, a voltage of up to approximately DC 400 V is applied to the plurality of switches 120 which are turned off. Thus, the plurality of switches 120 are required to withstand a voltage of DC 400 V or more. Accordingly, the plurality of switches 120 are required to be large-sized expensive switches which withstand a high voltage and the number of those switches is required to be at least as many as the number of all the output terminals of the battery blocks 111.
According to one aspect of the present invention, a battery voltage measurement device includes: a plurality of first switching sections, in which each pair of adjacent first switching sections sequentially selects two output terminals of each of a plurality of battery blocks included in a battery pack so that each of the selected output terminals are connected to one of a pair of conductor wires; a voltage detection section for detecting a battery voltage of each of the plurality of battery blocks via the pair of conductor wires; and second switch sections each being provided on a respective one of the pair of conductor lines and being serially connected to each group of the plurality of first switch sections connected in parallel to one of the pair of conductor lines.
With the above-described structure, by providing the series circuit in which the plurality of the first switching sections are connected to the second switching sections, the voltage of up to approximately DC 400 V applied to the first and second switching sections being in an off state, is applied to the first and second switching sections as voltages divided by the respective parasitic capacitance of the first and second switching sections being in an off state, so that the voltage applied to the first and second switching section can be lowered. Thus, small-sized inexpensive switches only required to withstand a voltage which is lower than that conventionally-required to withstand can be used as the first and second switching sections. Although the first switching sections are conventionally required to withstand a voltage of DC 400 V or more, by equalizing the respective parasitic capacitance of the first and second switching sections, a voltage which the first and second switching sections are required to withstand can be lowered to approximately DC 200 V. Moreover, by controlling the parasitic capacitance of the first and second switching sections, a voltage which the first switching sections are required to withstand can be lowered and an electric circuit of the voltage measurement section can be structured (as an IC chip) using a conventional IC process.
According to one embodiment of the invention, the battery voltage measurement device may further include: a capacitance section laid between the pair of conductor lines for selectively storing a battery voltage of each of the battery blocks via the first and second switching sections; and a third switching section for selectively applying the battery voltage stored in the capacitance section to the voltage detection section, in which the voltage detection section may detect the battery voltage stored in the capacitance section via the third switching section.
With the above-described structure, by providing the series circuit in which the first switching sections are connected to the second switching sections, in the case where a battery voltage of a designated battery block is stored in a capacitor section and thereafter all of the first and second switching sections are turned off, at the time of measuring the battery voltage, when the third switching sections are turned on, a voltage of up to approximately DC 400 V of a battery pack is divided by parasitic capacitance of the first and second switching sections being in an off state and is applied to the first and second switching sections, so that the voltage applied to the plurality of first and second switching sections can be lowered. Thus, small-sized inexpensive switches only required to withstand a voltage which is lower than that conventionally-required to be withstood can be used as the first and second switching sections. Although the first switching sections are conventionally required to withstand a voltage of DC 400 V or more, by equalizing the respective parasitic capacitance of the first and second switching sections, a voltage which the first and second switching sections are required to withstand can be lowered to approximately DC 200 V.
According to another embodiment of the invention, the third switching section may include a plurality of serially-connected switching sections.
With the above-described structure, by providing the third switching sections including a plurality of serially-connected switches, when the third switching sections are turned off and the designated first switching sections and the second switching sections serially connected thereto are turned on so as to store a battery voltage of a designated battery block in the capacitor section, the voltage of up to approximately DC 400 V of the battery pack is divided by parasitic capacitance of the plurality of serially-connected switches (the third switching sections) and is applied to each of the third switching sections, so that each voltage applied to the plurality of serially-connected switches (the third switching sections) can be lowered. Thus, small-sized inexpensive switches only required to withstand a voltage which is lower than that conventionally-required to be withstood can be used as the third switching sections. Moreover, an IC chip including the third switching sections can be manufactured using a conventional IC process.
According to still another embodiment of the invention, the second switching section may be one switch or may include a plurality of serially-connected switches.
With the above-described structure, small-sized inexpensive switches only required to withstand a voltage which is lower than that conventionally-required to be withstood can be used as the first switching sections. Specifically, by providing two sets of the second switching sections serially connected to the first switching sections, the two sets of the second switching sections are only required to withstand a voltage of approximately DC 200 V, and by providing four sets of the second switching sections serially connected to the first switching sections, the four sets of the second switching sections are only required to withstand a voltage of approximately DC 100 V. approximately DC 80 V. By further lowering a voltage which the first switching sections are required to withstand, existing semiconductor switches can be used as the first switching sections, and an IC chip including the first switching sections can be readily manufactured using a conventional IC process.
According to still another embodiment of the invention, a relationship between a parasitic capacitance Ca of the plurality of first switching sections connected in parallel to the pair of conductor lines and a parasitic capacitance Cb of the second switching sections may be represented by Caxe2x89xa7Cb.
With the above-described structure, when the relationship between the parasitic capacitance of groups of switches is represented by Cb less than Ca, since the number of the first switching sections is considerably greater than that of the second switching sections, a voltage applied to the first switching sections can be lower than that applied to the second switching sections, whereby it is possible to lower a voltage withstanding requirement of the first switching sections, the number of which is greater than that of the second switching sections.
According to still another embodiment of the invention, the battery voltage measurement device further includes overvoltage prevention sections each being connected to a respective one of the pair of conductor lines, which serially connect the first switching sections to the second switching sections, in a forward direction from two output terminals of a designated battery block.
With the above-described structure, a voltage is applied from an output terminal of a designated battery block to a pair of conductor lines laid between serially-connected switches, so that a voltage clamp function of the rectifier sections which prevents a voltage from being excessive with respect to a voltage withstanding requirement of the switches can be attained.
According to another aspect of the present invention, a battery voltage measurement device includes: a battery pack including a plurality of battery blocks; a plurality of first switching sections, wherein each pair of adjacent first switching sections sequentially selects two output terminals of each of the plurality of battery blocks so that each of the selected output terminals are connected to a respective one of a pair of conductor wires; a voltage detection section for detecting a battery voltage of each of the plurality of battery blocks via the pair of conductor wires; and second switch sections each being provided on a respective one of the pair of conductor lines and being serially connected to each group of the plurality of first switch sections connected in parallel to one of the pair of conductor lines.
According to one embodiment of the invention, the battery voltage measurement device may further include: a capacitance section laid between the pair of conductor lines for selectively storing a battery voltage of each of the battery blocks via the first and second switching sections; and a third switching section for selectively applying the battery voltage stored in the capacitance section to the voltage detection section, in which the voltage detection section detects the battery voltage stored in the capacitance section via the third switching section.
According to another embodiment of the invention, the third switching section may include a plurality of serially-connected switching sections.
According to still another embodiment of the invention, the second switching section may include a plurality of serially-connected switching sections.
According to still another embodiment of the invention, a relationship between a parasitic capacitance Ca of the plurality of first switching sections connected in parallel to the pair of conductor lines and a parasitic capacitance Cb of the second switching sections may be represented by Caxe2x89xa7Cb.
According to still another embodiment of the invention, the battery voltage measurement device may further include overvoltage prevention sections each being connected to a respective one of the pair of conductor lines, which serially connect the first switching sections to the second switching sections, in a forward direction from two output terminals of a designated battery block.
Thus, the invention described herein makes possible the advantages of providing a battery voltage measurement device which can lower a voltage withstanding requirement of switches, so that small-sized inexpensive switches can be used.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.